A plasma processing apparatus generates a plasma in a chamber which can be used to treat a workpiece supported by a platen in a process chamber. In some embodiments, the chamber in which the plasma is generated is the process chamber. Such plasma processing apparatus may include, but not be limited to, doping systems, etching systems, and deposition systems. In some plasma processing apparatus, ions from the plasma are attracted towards a workpiece. In a plasma doping apparatus, ions may be attracted with sufficient energy to be implanted into the physical structure of the workpiece, e.g., a semiconductor substrate in one instance.
In other embodiments, the plasma may be generated in one chamber, which ions are extracted from, and the workpiece is treated in a different process chamber. One example of such a configuration may be a beam line ion implanter where the ion source utilizes an inductively coupled plasma (ICP) source. The plasma is generally a quasi-neutral collection of ions (usually having a positive charge) and electrons (having a negative charge). The plasma has an electric field of about 0 volts per centimeter in the bulk of the plasma.
Turning to FIG. 1, a block diagram of one exemplary plasma doping apparatus 100 is illustrated. The plasma doping apparatus 100 includes a process chamber 102 defining an enclosed volume 103. A gas source 104 provides a primary dopant gas to the enclosed volume 103 of the process chamber 102 through the mass flow controller 106. A gas baffle 170 may be positioned in the process chamber 102 to deflect the flow of gas from the gas source 104. A pressure gauge 108 measures the pressure inside the process chamber 102. A vacuum pump 112 evacuates exhausts from the process chamber 102 through an exhaust port 110. An exhaust valve 114 controls the exhaust conductance through the exhaust port 110.
The plasma doping apparatus 100 may further includes a gas pressure controller 116 that is electrically connected to the mass flow controller 106, the pressure gauge 108, and the exhaust valve 114. The gas pressure controller 116 may be configured to maintain a desired pressure in the process chamber 102 by controlling either the exhaust conductance with the exhaust valve 114 or a process gas flow rate with the mass flow controller 106 in a feedback loop that is responsive to the pressure gauge 108.
The process chamber 102 may have a chamber top 118 that includes a first section 120 formed of a dielectric material that extends in a generally horizontal direction. The chamber top 118 also includes a second section 122 formed of a dielectric material that extends a height from the first section 120 in a generally vertical direction. The chamber top 118 further includes a lid 124 formed of an electrically and thermally conductive material that extends across the second section 122 in a horizontal direction.
The plasma doping apparatus further includes a source 101 configured to generate a plasma 140 within the process chamber 102. The source 101 may include a RF source 150 such as a power supply to supply RF power to either one or both of the planar antenna 126 and the helical antenna 146 to generate the plasma 140. The RF source 150 may be coupled to the antennas 126, 146 by an impedance matching network 152 that matches the output impedance of the RF source 150 to the impedance of the RF antennas 126, 146 in order to maximize the power transferred from the RF source 150 to the RF antennas 126, 146.
In some embodiments, the planar and helical antennas 126, 146 comprise a conductive material wound in a spiraling pattern. For example, FIG. 2A shows one embodiment of a traditional planar antenna 126, while FIG. 2B shows a second embodiment. FIG. 3 shows a traditional helical antenna 146.
The plasma doping apparatus may also include a bias power supply 190 electrically coupled to the platen 134. The plasma doping system may further include a controller 156 and a user interface system 158. The controller 156 can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller 156 may also include communication devices, data storage devices, and software. The user interface system 158 may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma doping apparatus via the controller 156. A shield ring 194 may be disposed around the platen 134 to improve the uniformity of implanted ion distribution near the edge of the workpiece 138. One or more Faraday sensors such as Faraday cup 199 may also be positioned in the shield ring 194 to sense ion beam current.
In operation, the gas source 104 supplies a primary dopant gas containing a desired dopant for implantation into the workpiece 138. The source 101 is configured to generate the plasma 140 within the process chamber 102. The source 101 may be controlled by the controller 156. To generate the plasma 140, the RF source 150 resonates RF currents in at least one of the RF antennas 126, 146 to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber 102. The RF currents in the process chamber 102 excite and ionize the primary dopant gas to generate the plasma 140.
The bias power supply 190 provides a pulsed platen signal having a pulse ON and OFF periods to bias the platen 134 and hence the workpiece 138 to accelerate ions 109 from the plasma 140 towards the workpiece 138. The ions 109 may be positively charged ions and hence the pulse ON periods of the pulsed platen signal may be negative voltage pulses with respect to the process chamber 102 to attract the positively charged ions. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy.
One drawback of conventional plasma processing is lack of plasma uniformity. In some embodiments, the plasma concentration is greater in a portion of the process chamber, thereby causing unequal implantation of ions. To overcome this, it has been suggested to add a conductive body near the antenna 126, 146. Note in FIGS. 2 and 3, the antenna can be viewed as a set of connected nearly circular coiled segments, where the first end of a first coiled segment is connected to the second end of an adjacent coiled segment. For example, both FIG. 2A and FIG. 2B can be seen to have 4 connected coiled segments. In the case of FIG. 2A, the shape of each coiled segment 201 is slightly irregular such that the second end of a coiled segment 201 does not meet the first end of that coiled segment. Thus, one end of coiled segment 201a connects to an end of coiled segment 201b. In contrast, the coiled segments 202 of FIG. 2B are circular, however, there is a break such that the two ends of the coiled segments 202 do not connect. In this case, a linear segment 203 is used to connect two adjacent coiled segments 202. For example, linear segment 203a is used to connect coiled segment 202d and coiled segment 202c. 
FIG. 3 shows a helical antenna 146. The wound coiled segments 204 of a helical antenna 146 can be attached using the mechanisms shown in FIG. 2A-B for planar antennas. To improve the plasma uniformity of a chamber utilizing such an antenna, it has been suggested to add a conductive body near one of more coiled segments of the antenna. In other words, referring to FIG. 2A, a metal object may be shaped and located so as to affect coiled segment 201d, without little or no impact on the other coiled segments. Stated another way, the conductive body is symmetrical in the radial direction (assuming a polar coordinate system where the origin is the center of the antenna as shown in FIGS. 2A-B). The metal object may be circular or annular. For example, an annular metal body may be used to affect coiled segment 201a, without affecting coiled segments 201b-d. 
FIG. 4 shows a block diagram of a conventional ion implanter 300. Of course, many different ion implanters may be used. The conventional ion implanter may comprise an ion source 302 that may be biased by a power supply 301. The system may be controlled by controller 320. The operator communicates with the controller 320 via user interface system 322. The ion source 302 is typically contained in a vacuum chamber known as a source housing (not shown). The ion implanter system 300 may also comprise a series of beam-line components through which ions 10 pass. The series of beam-line components may include, for example, extraction electrodes 304, a 90° magnet analyzer 306, a first deceleration (D1) stage 308, a 70° magnet collimator 310, and a second deceleration (D2) stage 312. Much like a series of optical lenses that manipulate a light beam, the beam-line components can manipulate and focus the ion beam 10 before steering it towards a workpiece or wafer 314, which is disposed on a workpiece support 316.
In operation, a workpiece handling robot (not shown) disposes the workpiece 314 on the workpiece support 316 that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source 302 and extracted by the extraction electrodes 304. The extracted ions 10 travel in a beam-like state along the beam-line components and implanted on the workpiece 314. After implanting ions is completed, the workpiece handling robot may remove the workpiece 314 from the workpiece support 316 and from the ion implanter 300.
The ion source 302 may be an inductively coupled plasma (ICP) ion source. In some embodiments, such as in FIGS. 5A-B, the ion source 302 may comprise a rectangular enclosure, having an extraction slit 335 on one side 337. In certain embodiments, the side 336 opposite the extraction slit 335 may be made of a dielectric material, such as alumina, such that a planar antenna 338 may be placed against the dielectric wall 336 to create a plasma within the enclosure 302. The enclosure 302 also has a top surface 339, a bottom surface 341, and two endwalls 338, 340.
In another embodiment, a helical antenna 350 is wrapped around the endwalls 338, 340 and the top surface 339 and bottom surface 341 of the ICP ion source 302, as shown in FIG. 6.
In these embodiments, due to the irregular shape of the ion source 302, it is difficult to create a uniform plasma which can be extracted through the extraction slit 335. Accordingly, there is a need for a plasma processing method that overcomes the above-described inadequacies and shortcomings.